1. Field of the Invention
The present invention relates to a plasticizing apparatus used for a pre-plasticization-type injection molding machine in order to plasticize and melt a molding material and to supply the melted material to an injection apparatus.
2. Description of the Related Art
Conventionally, a so-called pre-plasticization-type injection molding machine is known (see Japanese Patent Application Laid-Open (kokai) No. 8(1996)-25437. Such an injection molding machine includes a plasticizing apparatus for plasticizing and melting a molding material, and an injection apparatus for injecting and charging melted resin into a mold.
In such a pre-plasticization-type injection molding machine, a molding material is supplied from a hopper to the interior of a barrel of the plasticizing apparatus, and the molding material is plasticized (melted) by rotation of a screw disposed within the barrel. The thus-melted resin is discharged from a resin exit provided at the tip end of the barrel to be fed, via a resin passage portion, to the interior of the tip end portion of an injection cylinder of the injection apparatus. The thus-fed resin is measured and accumulated within the injection cylinder. During measurement, an injection plunger of the injection cylinder retracts. After completion of measurement, the injection plunger is advanced in order to inject and charge the resin into a cavity of a mold.
The pre-plasticization-type injection molding machine involves a problem in that during injection, the measured resin flows backward via the resin passage portion to the interior of the barrel. Therefore, a valve section is added to the resin passage portion in order to open and close the resin passage. During measurement, the valve section is opened in order to allow passage of resin, and during injection, the valve section is closed in order to shut off the resin passage, thereby preventing backflow of the resin at the resin passage portion.
However, such a conventional pre-plasticization-type injection molding machine has the following drawbacks to be solved.
First, since only a valve of a limited type can be used for the valve section, the valve section cannot be opened and closed instantaneously (within a short period of time), resulting in the occurrence of lost time in relation to the opening and closing operations of the valve section. Therefore, molding cycle time cannot be shortened, and productivity cannot be improved.
Second, a valve section is added to the resin passage portion, and a drive section for opening and closing the valve section is provided. Therefore, the resin passage portion must be formed to have a special internal structure and shape. This results in a complex structure of the resin passage portion, decreased reliability, and increased cost.
An object of the present invention is to provide a plasticizing apparatus used for a pre-plasticization-type injection molding machine which can open and close a resin passage instantaneously (within a short period of time) to thereby shorten molding cycle time and improve productivity.
Another object of the present invention is to provide a plasticizing apparatus used for a pre-plasticization-type injection molding machine which can simplify the structure of the resin passage portion to thereby improve reliability, while decreasing overall cost of the pre-plasticization-type injection molding machine.
To achieve the above-described objects, the present invention provides a plasticizing apparatus used for a pre-plasticization-type injection molding machine in which a molding material is plasticized/melted by rotation of a screw disposed within a barrel and is then supplied to an injection apparatus; and a screw drive section is provided in order to open and close a resin passage of the barrel by axial displacement of the screw. The plasticizing apparatus is characterized in that the screw drive section comprises a rotational drive section supported in an axially moveable manner and adapted to rotate the screw; and an advancement/retraction drive section including a servomotor and a ball-screw mechanism for converting rotational motion of the servomotor to linear motion in order to axially move the rotational drive section.
By virtue of the above-described structure, the screw disposed within the barrel is rotated by the rotational drive section of the screw drive section, so that the molding material within the barrel is plasticized (melted) and is then supplied to the injection apparatus. Further, the rotational drive section (screw) is advanced and retracted by the advancement/retraction section of the screw drive section, so that the resin passage of the barrel is opened and closed in accordance with the position of the screw.